8-bit Microcontrollers中的主题 Re: HC908QY4A A very peculiar bug

HC908QY4A A very peculiar bug

bigmac — Thu, 24 Jul 2008 22:28:39 GMT

Hello all,

Background -

I am using a QY4A device, in conjunction with assembly code, to decode an on-off keyed (OOK) signal that is output from a wireless receiver. This signal is connected to the external IRQ pin. The decode algorithm makes use of a pair of sub-routines that will exit when a change of state occurs, or after a timeout period has elapsed. The sub-routines are designed to ignore short noise pulses from the receiver.

The assembly code for one of the sub-routines is attached. The other sub-routine is similar, except that it handles signal transitions of the opposite polarity. The attached code operates as expected, and the decoding process is successful.

However, when I attempted to replace the pair of instructions

DEC 1,SP

BNE WL0

with the single instruction

DBNZ 1,SP,WL0

the decoding process failed. I tried preceeding the line with a couple of NOPs, so as to retain the same number of cycles, but to no avail. It is as though the branch is always taken, or never taken - I can't be certain which one. Full chip simulation gives the expected result.

I wonder if anyone else has experienced a similar problem. It has certainly involved some head scratching for the last few days - perhaps I am missing something obvious.

Regards,

Mac

Re: HC908QY4A A very peculiar bug

tonyp — Thu, 29 Oct 2020 09:24:23 GMT

Your code says:

; On exit, ZF = 1 if timeout occurred.

DBNZ instructions do NOT affect the Z flag.  Could this be it?

Re: HC908QY4A A very peculiar bug

JimDon — Thu, 29 Oct 2020 09:24:25 GMT

The only difference I see between DEC and DBNZ is that DEC affects the conditions code and DBNZ does not.

You comments says:

; On exit, ZF = 1 if timeout occurred.

So perhaps this is it...

Re: HC908QY4A A very peculiar bug

bigmac — Fri, 25 Jul 2008 00:31:11 GMT

Hello Tony P and Jim D,

Thank you for pointing out the problem - I think a question of not seeing the wood for the trees. Yes I do test the Z-flag to determine whether timout had occurred, or not.

Regards,

Mac